1. Field of the Invention
The present invention relates to an orally administrable and stable solution containing as an active ingredient Methoxsalen (8-methoxyfuro-[3,,2, 6,7]-coumarin) of the formula ##STR2## useful in the photochemotherapy of psoriasis, to a process for the preparation thereof and to a process for the use thereof.
2. Background of the Invention
In the oral application of Methoxsalen in solid form, usually up to now (as tablets or capsules containing the powdery active ingredient) the patient ma be subjected to irradiation only after two hours after administration of the medicament (Wien.Klin.Wschr., 89, Suppl. 75 (1977)), which fact is complicated and time-consuming both for the physician and for the patient. Furthermore, levels of Methoxsalen of different height appear in the patient's blood, so that the optimum duration of the irradiation varies between single treatments even with the same patient. Therefore, there is a demand for a form of administration which enables the blood level of Methoxsalen required for the irradiation to be available within a shorter period of time and at a height substantially equal each time. Up to now no adequate preparation has been available to achieve this.
Methoxsalen is a substance which is soluble in most solvents to a small extent. It is quite soluble in chloroform and in aqueous alkali, but these two solvents cannot be used for the preparation of a solution suitable for oral administration which can be filled into capsules Furthermore, an alkaline medium results in the cleavage of the coumarin ring. If Methoxsalen is dissolved in a pharmaceutically useful, but aqueous solvent, frequently a yellow coloring develops during storage. Additionally, in case of a higher content of water a precipitate is formed. Further some anhydrous solvents can not be employed without irritations due to their hygroscopic properties.